1. Field of the Invention
The present invention relates to an engine lubrication system in which the base of a crankcase supporting a crankshaft forms an oil reservoir, a part of an oil slinger that is driven by the crankshaft via a transmission system is immersed in oil within the oil reservoir, and the interior of the engine is lubricated with splashed oil generated by rotation of the oil slinger.
2. Description of the Related Art
A splash-type lubrication system employing an oil slinger is known in, for example, Japanese Utility Model Registration Application Laid-open No. 62-34108. A forced lubrication system is also known in, for example, Japanese Patent Registration No. 2772794. In a forced lubrication system, oil that is drawn from an oil reservoir is fed by pressure using an oil pump to all the sections of an engine that are to be lubricated, such as the circumference of a crankshaft and a valve-operating mechanism.
The splash-type lubrication system has a simple structure and can be obtained at a comparatively low cost. However, since a transmission system for driving the oil slinger is connected to a crankshaft, it is generally difficult to arrange the oil slinger in the central area of the oil reservoir. It is therefore necessary for the amount of oil that is stored in the oil reservoir to be set at an adequate level so that the oil slinger is not exposed above the liquid level even when the engine is operated in a tilted state. As a result, when the engine is operated in a normal horizontal state, the oil slinger is immersed in the oil at too great an extent, thereby causing a loss of motive power due to the resistance in stirring of the oil slinger.
In the forced lubrication system, oil discharged from the oil pump can be supplied to all the sections of the engine that are to be lubricated without being influenced by changes in the operational attitude of the engine. However, such an oil pump that can supply oil to all the sections of the engine that are to be lubricated inevitably has a large capacity, thereby increasing the cost.
The present invention has been carried out in view of the above-mentioned circumstances. It is an object of the present invention to provide an engine lubrication system based on a splash-type lubrication system which, in order to compensate for the drawbacks thereof, is combined with a forced-type lubrication system. As a result of the present invention, the capacity of the oil pump is reduced and the drive system is simplified, thereby effectively avoiding an increase in the overall cost of the engine.
In order to accomplish the above-mentioned object, in accordance with a first aspect of the present invention, there is proposed an engine lubrication system in which the base of a crankcase supporting a crankshaft forms an oil reservoir. A part of an oil slinger that is driven by the crankshaft via a transmission system is immersed in oil within the oil reservoir, and the interior of the engine is lubricated with splashed oil generated by rotation of the oil slinger. An oil pump that is driven by the transmission system is immersed in the oil within the oil reservoir, and a discharge port of the oil pump communicates with a lubricating-oil passage within the crankshaft.
In accordance with the above-mentioned first aspect, even if the extent to which the oil slinger is immersed in the oil becomes extremely low when the engine is operated in a tilted state, and the amount of splashed oil decreases, since the oil pump, which is completely immersed in the oil within the oil reservoir, operates to continuously supply the oil to the crankshaft, the sections of the crankshaft that bear a high load can still be provided with forced lubrication, and operation of the engine can be carried out continuously without any problems. It is therefore possible to set the amount of oil stored in the oil reservoir as low as possible without taking the engine tilt attitude into consideration, thereby achieving a reduction in the loss of motive power due to the resistance in stirring of the oil slinger.
Furthermore, since the oil pump is employed only for lubrication of the circumference of the crankshaft, a pump with a comparatively small capacity will suffice and can be obtained at a low cost. Moreover, since the oil pump is driven using the transmission system that drives the oil slinger, it is unnecessary to employ a transmission system exclusively used for the oil pump. It is therefore possible to effectively avoid an increase in the cost of the engine despite the combined use of forced lubrication.
Furthermore, in accordance with a second aspect of the present invention, there is proposed an engine lubrication system wherein the crankcase is equipped with an oil filter, a first oil pipe and a second oil pipe. The first oil pipe and the second oil pipe are disposed within the crankcase. The first oil pipe connects the discharge port of the oil pump to a crankcase inlet port which communicates with an unpurified chamber of the oil filter, while the second oil pipe connects the lubricating-oil passage to a crankcase outlet port which communicates with a purified chamber of the oil filter.
In accordance with the above-mentioned second aspect, even when there is oil leakage from the first and second oil pipes and the joints thereof, the leaked oil is returned immediately to the oil reservoir, thereby reliably preventing leakage to the outside.
Furthermore, in accordance with a third aspect of the present invention, there is proposed an engine lubrication system wherein an oil pressure sensor is connected to an oil passage that communicates with the discharge port of the oil pump. The oil pressure sensor generates an alert signal when the discharge pressure of the oil pump becomes equal to or less than a predetermined value during operation of the engine. A leak hole is provided in a side wall of an intake port of the oil pump. The leak hole is exposed above the liquid level when the liquid level of the oil reservoir becomes equal to or less than a predetermined alert level.
In accordance with the above-mentioned third aspect, when the liquid level of the oil reservoir drops to the alert level or below the alert level, the leak hole in the oil pump, communicates with the intake port of the oil pump is exposed above the liquid level of the oil reservoir. Air is therefore taken into the crankcase through the leak hole, and the discharge pressure thereby becomes equal to or less than the predetermined value. The oil pressure sensor detects the decrease in the discharge pressure and then operates its alerting device, thereby informing the operator of the need for the oil reservoir to be replenished with oil.
Furthermore, in addition to the above-mentioned third aspect, in accordance with a fourth aspect of the present invention, there is proposed an engine lubrication system wherein the oil slinger is arranged so that a lower end thereof is positioned beneath the leak hole.
In accordance with the above-mentioned fourth aspect, even during the above-mentioned alert state, the oil slinger can still splash oil and continue splash-lubrication.
The above-mentioned object, other objects, characteristics and advantages of the present invention will become apparent from an explanation of a preferred embodiment that will be described in detail below by reference to the appended drawings.